Load sharing in SS7 networks

ABSTRACT

A service indicator SI field is used for load sharing in SS7 networks, in addition to the service link selection SLS field. If there are only two links or connections between two points of the SS7 network, load sharing can also be performed on the basis of the SI field only.

CLAIM FOR PRIORITY

[0001] This application claims the benefit of priority to U.S.Provisional Application Serial No. 60/403,654, which was filed on Aug.16, 2002, the contents of which are hereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

[0002] The present invention relates to load sharing in networks, and inparticular, to a system and method for load sharing for links or linksets between a first signaling point and a second signaling point incommunications networks.

BACKGROUND OF THE INVENTION

[0003] In communications networks in which the central Signaling SystemNo. 7 standardized by the International Telecommunication Union ITU orCommon Channel Signaling System 7 CCS7, also called SS7, conforming tothe ITU-T Q.700 Recommendations and following is used for transmittingmessages, the communication between two signaling points SP, i.e. nodesand/or end points of the communications network, takes place viaconnections which in this context are called signaling links or SS7links. A node is also referred to as a signaling transfer point STP,whereas an end point, in contrast, is also referred to as a signalingend point SEP.

[0004] As described in ITU-T Q.700ff, it is possible in SS7communications networks to combine signaling links into so-calledsignaling link sets. Each signaling link set comprises at least onesignaling link.

[0005] The architecture of SS7 is also described in ITU-T Q.700ff. Adistinction is made between different protocol layers, called levels inthis context. Levels 1-3 form the Message Transfer Part MTP. A number ofLevel 4 protocols are defined in SS7 and here are called User Parts UP.Examples of these are the Telephone User Part TUP, the ISDN User PartISUP or the Signaling Connection Control Part SCCP. Messages of theseUser Parts are transferred securely by the MTP. In this case a so-calledservice indicator SI is used in order to distinguish the individual UserParts. The SI is a 4-bit value; the following assignment to the UserParts applies (extract shown): SI MTP User 0 Signaling NetworkManagement Messages (SNM) 1 Maintenance Regular Messages (MTN) 2Maintenance Special Messages (MTNS) 3 Signaling Connection Control Part(SCCP) 4 Telephone User Part (TUP) 5 ISDN User Part (ISUP) 6 Data UserPart (call and circuit-related messages) 7 Data User Part (facilityregistration/cancellation messages) 8 MTP Testing User Part

[0006] The MTP, particularly MTP Level 3, also handles theadministration of the links. If there are multiple link sets and/ormultiple links between two signaling points, load distribution or loadsharing, among other functions, is effected by MTP Level 3 on the basisof the so-called signaling link selection field SLS, described in ITU-TQ.704. The SLS value is part of the so-called routing label and has alength of 4 bits.

[0007] In known SS7 implementations, load sharing has been carried outuntil now solely on the basis of the value included in the SLS field.This is insufficient in certain application scenarios, however. In ITU-TQ.700 Section 3.2.1 and in ITU-T Q.704 Section 2.3.1 it is mentioned ineach case that the routing of messages, though not load sharing, canalso be performed on the basis of the service indicator SI.

SUMMARY OF THE INVENTION

[0008] The present invention discloses a system and method for loaddistribution or for load sharing in SS7 networks which is based on theservice indicator and which involves low implementation overhead.

[0009] One aspect of the present invention is that the SI field which isincluded in the MTP header of the message signaling unit MSU is alsoused for load sharing in SS7 networks in addition to the normally usedSLS field included in the routing label of messages or message signalingunits MSU. If there are only two links or connections between two pointsof the SS7 network, then load sharing can also be effected on the basisof the SI field.

[0010] One advantage is that the SI field is representative of the UserPart of the MSU and therefore load sharing can be performed based on theUser Part of the MSU. According to the above table, the serviceindicator SI “5”=“0101B” is provided, for example, for the ISDN UserPart ISUP, whereas an SI “3”=“0011B” is used for the SignalingConnection Control Part SCCP. As can be read from the specified binaryrepresentation of the SI values for SCCP and ISUP, it is possible todistinguish these two User Parts by evaluation of the bits with asignificance of “2” or “4”, i.e. Bit 2 ¹ or 2 ².

[0011] Load sharing based on the User Part of an MSU has in turn anumber of advantages. One of these advantages is that, for example,separate links and/or link sets can be provided for SCCP messages andfor ISUP messages. SCCP messages are longer on average than ISUPmessages, with the result that send buffers of signaling points are moreheavily loaded by SCCP messages than by ISUP messages. This can lead inturn to ISUP messages being obstructed or delayed by SCCP messages.However, this should be avoided in application situations in which ISUPmessages are assigned a higher priority than SCCP messages. This isadvantageously achieved by the present invention.

[0012] A further advantage is based on the fact that with conventionalload sharing the traffic can be distributed over only 16 links, sincethe SLS value is a 4-bit value. This number can be expanded by using theSI field, which also comprises 4 bits. The already mentioned distinctionbetween SCCP and ISUP messages, for example, results in a doubling ofthe number to 32 possible links or link sets, consisting of 16 for ISUPmessages and 16 for SCCP messages.

[0013] The invention can advantageously be used in conjunction withother methods which extend the address space opened up by the SLS field,in which case the number of possible links/link sets is then doubledonce again, for example when a distinction is made between SCCP and ISUPmessages.

[0014] Except for the implementation of the improved load sharingmethod, the invention requires no modifications to be made to componentsof the communications network and can therefore be implemented easilyand cost-effectively. In particular, the method relates to the sendingcomponent(s); no provision needs to be made for modifications to thereceiving component(s).

[0015] Through evaluation of the SI field, which is part of the serviceinformation octet SIO, which is in turn part of the MTP header, loadsharing in accordance with the transported protocol layers or User Partscan be performed quickly and without analysis of the protocol layerstransported by means of the MTP. This coding which is fixed for eachmessage has the advantageous consequence that an evaluation can belargely hardware-based and is therefore particularly suitable for use insignaling points, more particularly in signaling transfer points, forwhich there are high requirements in terms of throughput and messagetransmission delays.

[0016] According to the invention, a network element is also providedwhich comprises means for performing the inventive load sharing method.

[0017] The method according to the invention can advantageously be usedwithout any problem in conjunction with other load sharing methods. If aconventional load sharing method includes, for example, the following:

[0018] (a) Generate a list of possible link sets to the desireddestination, for example on the basis of the SS7 destination point codeDPC,

[0019] (b) Select one of the link sets; in traditional implementationsthis is done solely on the basis of the SLS value, whereas in morerecent implementations, in contrast, it is also done for example on thebasis of further fields of an MSU,

[0020] (c) Select a link within the link set selected in step (b), forexample again on the basis of the SLS value and/or of further fields,where other bit positions of the fields considered are usually used forsteps (b) and (c) so that steps (b) and (c) are independent of eachother,

[0021] then, according to the invention, the selection of the link setsor links can be made additionally or exclusively on the basis of the SIfield, the rest of the selection method remaining untouched.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention is explained in more detail below as an exemplaryembodiment with reference to the figures.

[0023]FIG. 1A shows a first signaling point connected to a secondsignaling point by means of four further signaling points.

[0024]FIG. 1B shows another embodiment of the arrangement from FIG. 1A.

DETAILED DESCRIPTION OF THE INVENTION

[0025]FIG. 1 shows two typical network arrangements. In FIG. 1A, a firstsignaling point SP A is connected to a second signaling point F by meansof four further signaling points SP B, SP C, SP D, SP E. Four link setsLS0, LS1, LS2, LS3 are used to establish the connection between SP A andthe further signaling points SP B..E. In this arrangement, each of thelink sets comprises two links L00, L01 and L10, L11 and L20, L21 andL30, L31. The connections between SP F and the further signaling pointsSP B..E can be implemented as desired.

[0026] The arrangement in FIG. 1B corresponds to the arrangement fromFIG. 1A, albeit with the omission of SP D and SP E as well as LS2 andLS3 and their assigned links L20, L21 and L30, L31.

[0027] The cited SP A and SP F can be signaling end points SEP orsignaling transfer points STP. This is of no significance for thepresent invention, however. With regard to the communication between SPA and SP F., the further signaling points SP B, SP C, SP D, SP E aresignaling transfer points STP.

[0028] The representation of the link sets as comprising two links ineach case is intended to serve only as an example. In other embodimentsthe link sets comprise an arbitrary number of links, while the number oflinks for different link sets may also be different.

[0029] In an advantageous embodiment, SP B, SP C, and also SP D, SP E,represented as different STPs, as shown by the dashed lines in FIG. 1,can also be combined into functional units B′, D′. Although the unitsB′, D′ each have two point codes PC, in practical configurations theunits B′, D′ can be implemented as a unified signaling point, which canresult in a situation in which there are two link sets associated withone node B′, D′.

[0030] By way of example it will be described in the following, withreference to the structures in FIGS. 1A and 1B, how a distinction can bemade and load sharing implemented between ISUP and SCCP traffic. Bymeans of the present invention it is possible to realize load sharingbetween STPs SP B..E. The sending of MSUs by SP A to SP F will beconsidered below.

[0031] First, the possible link sets LS0, . . . , LS3 for transferringMSUs from SP A to SP F are determined and entered in a list LS at SP A.This process of determination can, as is known, be made on the basis ofthe point code of SP F, which is entered as a destination point code inan MSU. In the case represented in FIG. 1A, list LS is given by LS=[LS0,LS1, LS2, LS3]. In the example from FIG. 1B, list LS is given byLS=[LS0, LS1, LS0, LS1], in one embodiment also [LS0, LS1]. List LS isthe result of a first step.

[0032] For selection of the link set it is established on the basis ofspecifications applicable to SP A which bit of the 4-bit SLS value willbe evaluated in order to select a link set. These specifications arestored together with other administered data separately per destination,for example, in SP A.

[0033] The value of the bits of the SLS value that are to be evaluatedis designated by Bit(SLS) and is either 0 or 1. During the evaluation ofthe SI value the second or third bit of the SI value can simply be used(bit positions 2 ¹ or 2 ²) since these are different for SCCP and ISUP.The value of this bit is designated by Bit(SI).

[0034] The link set is selected by means of an indexed access to listLS, where 2*Bit(SLS)+Bit(SI) is used as the index.

[0035] If load sharing is to be executed over more than 4 link sets,more than one bit of the SLS value can be evaluated accordingly. Forload sharing via 2 link sets, as in the arrangement shown in FIG. 1B,the selection procedure can be simplified to the extent that theevaluation of the SLS value is omitted completely and one of the twolink sets is selected on the basis of the SI value.

[0036] If the bit with significance 2 ¹ of the SI value is used asBit(SI), the following selection table results for the case representedin FIG. 1A: LS Bit (SLS) Bit (SI) 0 0 0 = ISUP 1 0 1 = SCCP 2 1 0 = ISUP3 1 1 = SCCP

[0037] If the bit with significance 2 ² of the SI value is used asBit(SI), the following selection table results for the case representedin FIG. 1A: LS Bit (SLS) Bit (SI) 0 0 0 = SCCP 1 0 1 = ISUP 2 1 0 = SCCP3 1 1 = ISUP

[0038] Following selection of the link set, a link of the link set isselected by evaluation of a further bit of the SLS value. The process ofselecting a link remains the same compared with conventional methods,however.

[0039] If a link set fails or becomes active again following a failure,list LS changes. In an advantageous embodiment, link sets associatedwith the same unit B′, D′ are regarded as a pair. Accordingly, list LSfor the arrangement shown in FIG. 1A results in LS=[[LS0, LS1], [LS2,LS3]]. If one link set fails, it is replaced by the other link set ofthe pair. When a link set becomes active again following a failure, theold status is restored.

[0040] This has the advantage that, for example, the traffic previouslyswitched through unit B′ continues to be switched entirely through unitB′ if LS0 fails, since as a result of the described pair formation thestill active further connection to B′ is used as an alternate path withLS1. This avoids part of the traffic switched by B′ needing to be takenover by unit D′. Thus, the original balance between units B′ and D′ ispreserved.

[0041] If an entire pair fails, then the other pair is used. If aproblem with a link set occurs in this pair too, no further load sharingbetween link sets can take place, since list LS then includes one linkset.

[0042] It goes without saying that the present invention can also beused if an expansion of the “address space” opened up by the SLS fieldis provided by means of further fields of an MSU for load sharing overmore than 16 link sets or links.

[0043] The present invention can accordingly also be used in conjunctionwith “virtual SLS” or other methods which ensure that a suitable numberof bits that are still usable for load sharing are available for STPs inextensive SS7 networks.

[0044] Although described in connection with SCCP and ISUP, theinvention can also be applied without difficulty in conjunction with allother User Parts, for example in order to separate SCCP and TUP traffic.

[0045] If only one link set is provided, the selection method accordingto the invention can be used for the links that are then present (notshown).

[0046] The method according to the invention can be applied without anyproblem to all types of SS7 networks. It can be used most particularlyfor conventional SS7 networks in which classical time-multiplexed TDMlinks are used. The method according to the invention can also beapplied in particular to SS7 networks which are mapped by appropriatemethods to Internet Protocol IP networks in which, for example, IPconnections or IP links are therefore used instead of the TDM links andin which signaling points SP A..F are connected to a communicationsnetwork by means of IP. Other transport media or transport protocols forSS7 can likewise be used in conjunction with the present invention.

What is claimed is:
 1. A method for load sharing for links or link setsbetween a first signaling point and a second signaling point incommunications networks, comprising: providing Signaling System 7 forsignaling between signaling points; and connecting the first and thesecond signaling point via at least one signaling transfer point,wherein the load sharing is based on an evaluation of a serviceindicator in a routing label of messages.
 2. The method of claim 1,wherein the load sharing is additionally based on an evaluation of asignaling link selection field.
 3. The method of claim 1, wherein theload sharing is additionally based on an evaluation of additional fieldsof a message which is configured to be sent.
 4. A method for loadsharing for links or link sets between two adjacent signaling points incommunications networks, comprising: providing Signaling System 7 forsignaling between the signaling points; and basing the load sharing onan evaluation of a service indicator in a routing label of messages. 5.The method of claim 4, wherein the load sharing is additionally based onan evaluation of a signaling link selection field.
 6. The method ofclaim 5, wherein the load sharing is additionally based on an evaluationof additional fields of a message which is configured to be sent.
 7. Themethod according to claim 1, further comprising: determining, for amessage to be transmitted, a list of link sets for transmitting themessage to a destination, selecting and linking at least a portion ofbits of the service indicator field of the message to be transmitted toan index value of the list; and selecting the link set designated by theindex value in order to transmit the message.
 8. The method according toclaim 7, further comprising: selecting, among a plurality of signalinglinks of the selected link set one signaling link by repetition of thedetermining and selecting and linking for the signaling links of thelink set.
 9. The method according to claim 8, wherein in the selectingand linking at least the bit with significance “2” and/or the bit withsignificance “4” of the service indicator field are taken into account.10. The method according to claim 4, further comprising: determining,for a message to be transmitted, a list of link sets for transmittingthe message to a destination, selecting and linking at least a portionof bits of the service indicator field of the message to be transmittedto an index value of the list; and selecting the link set designated bythe index value in order to transmit the message.
 11. The methodaccording to claim 10, further comprising: selecting, among a pluralityof signaling links of the selected link set one signaling link byrepetition of the determining and selecting and linking for thesignaling links of the link set.
 12. The method according to claim 11,wherein in the selecting and linking at least the bit with significance“2” and/or the bit with significance “4” of the service indicator fieldare taken into account.
 13. The method according to claim 2, furthercomprising: determining, for a message configured to be transmitted, alist of link sets for transmitting the message to a destination;selecting and linking, at least a portion of bits of the signaling linkselection field and at least a portion of bits of the service indicatorfield of the message to be transmitted to an index value of the list;and selecting the link set designated by the index value in order totransmit the message.
 14. The method according to claim 13, furthercomprising: selecting, among a plurality of signaling links of theselected link set one signaling link by repetition of the determiningand selecting and linking for the signaling links of the link set. 15.The method according to claim 14, wherein in the selecting and linkingat least the bit with significance “2” and/or the bit with significance“4” of the service indicator field are taken into account.
 16. Themethod according to claim 5, further comprising: determining, for amessage configured to be transmitted, a list of link sets fortransmitting the message to a destination; selecting and linking, atleast a portion of bits of the signaling link selection field and atleast a portion of bits of the service indicator field of the message tobe transmitted to an index value of the list; and selecting the link setdesignated by the index value in order to transmit the message.
 17. Themethod according to claim 16, further comprising: selecting, among aplurality of signaling links of the selected link set one signaling linkby repetition of the determining and selecting and linking for thesignaling links of the link set.
 18. The method according to claim 17,wherein in the selecting and linking at least the bit with significance“2” and/or the bit with significance “4”, of the service indicator fieldare taken into account.
 19. The method according to claim 3, furthercomprising: determining, for a message configured to be transmitted, alist of link sets for transmitting the message to a destination;selecting and linking, at least a portion of bits of the signaling linkselection field and at least a portion of bits of the service indicatorfield and at least a portion of bits of additional field of the messageto be transmitted to an index value of the list; and selecting the linkset designated by the index value in order to transmit the message. 20.The method according to claim 10, further comprising: selecting, among aplurality of signaling links of the selected link set one signaling linkby repetition of the determining and selecting and linking for thesignaling links of the link set.
 21. The method according to claim 11,wherein in the selecting and linking at least the bit with significance“2” and/or the bit with significance “4” of the service indicator fieldare taken into account.
 22. The method according to claim 6, furthercomprising: determining, for a message configured to be transmitted, alist of link sets for transmitting the message to a destination;selecting and linking, at least a portion of bits of the signaling linkselection field and at least a portion of bits of the service indicatorfield and at least a portion of bits of additional field of the messageto be transmitted to an index value of the list; and selecting the linkset designated by the index value in order to transmit the message. 23.The method according to claim 22, further comprising: selecting, among aplurality of signaling links of the selected link set one signaling linkby repetition of the determining and selecting and linking for thesignaling links of the link set.
 24. The method according to claim 23,wherein in the selecting and linking at least the bit with significance“2” and/or the bit with significance “4” of the service indicator fieldare taken into account.
 25. The method according to claim 1, furthercomprising: determining, for a message to be transmitted, a list oflinks for transmitting the message to a destination; selecting andlinking, at least a portion of bits of the service indicator field ofthe message to be transmitted to an index value of the list; andselecting the link designated by the index value in order to transmitthe message.
 26. The method according to claim 4, further comprising:determining, for a message to be transmitted, a list of links fortransmitting the message to a destination; selecting and linking, atleast a portion of bits of the service indicator field of the message tobe transmitted to an index value of the list; and selecting the linkdesignated by the index value in order to transmit the message.
 27. Themethod according to claim 2, further comprising: determining, for amessage to be transmitted, a list of links for transmitting the messageto a destination; selecting and linking, at least a portion of bits ofthe signaling link selection field and at least a portion of bits of theservice indicator field of the message to be transmitted to an indexvalue of the list; and selecting the link designated by the index valuein order to transmit the message.
 28. The method according to claim 5,further comprising: determining, for a message to be transmitted, a listof links for transmitting the message to a destination; selecting andlinking, at least a portion of bits of the signaling link selectionfield and at least a portion of bits of the service indicator field ofthe message to be transmitted to an index value of the list; andselecting the link designated by the index value in order to transmitthe message.
 29. The method according to claim 3, further comprising:determining, for a message to be transmitted, a list of links fortransmitting the message to a destination; selecting and lining, atleast a portion of bits of the service indicator field and at least aportion of bits of the signaling link selection field and at least aportion of bits of additional fields of the message to be transmitted toan index value of the list; and selecting the link designated by theindex value in order to transmit the message.
 30. The method accordingto claim 6, further comprising: determining, for a message to betransmitted, a list of links for transmitting the message to adestination; selecting and lining, at least a portion of bits of theservice indicator field and at least a portion of bits of the signalinglink selection field and at least a portion of bits of additional fieldsof the message to be transmitted to an index value of the list; andselecting the link designated by the index value in order to transmitthe message.
 31. A signaling point for a Signaling System 7 network, thesignaling point connected to other signaling points of the network vialink sets, the link sets each comprising at least one link, thesignaling point with means for load sharing of outgoing messages oversaid links or link sets based on an evaluation of a service indicator ina routing label of messages.
 32. The signaling point of claim 31,further comprising means for load sharing of outgoing messages over saidlinks or link sets based on an evaluation of a signaling link selectionfield.
 33. A system for load sharing for links or link sets between afirst signaling point and a second signaling point in a communicationsnetwork, comprising a network element which provides signaling system 7for signaling between signaling points, connects the first and thesecond signaling point via at least one signaling transfer point,wherein the load sharing is based on an evaluation of a serviceindicator in a routing label of messages.